first Copa Libertadores game against Once Caldas aged 16, which made him one of the youngest players on debut for the tournament. After an impressive season with Cobreloa, Sánchez caught the attention of Serie A club Udinese, which signed him for a £1.7 million fee, on 21 April 2006. Udinese, however, began a maturation project with Sánchez and immediately loaned him to Chilean giants Colo-Colo in a season-long deal. Colo-Colo Sánchez debuted for Colo-Colo on 23 June 2006 in a 1–1 draw with Antofagasta; he scored his first goal on 29 October during the Chilean football derby against Universidad de Chile in a 4–2 win. His good performances allowed him to break into the starting lineup after successfully challenging veteran striker Mario Cáceres, and he then began partnering Humberto Suazo in the forward position. On 1 November, he scored a brace in a 4–4 league draw against Deportes La Serena. as well as his first continental goal in a 7–2 thrash over Alajuelense from Costa Rica for the Copa Sudamericana. Nevertheless, Colo-Colo was runner-up of that tournament after losing the final against Pachuca of Mexico. On 23 December 2006, Sánchez won his first professional title after being starter in the Torneo Clausura final against Audax Italiano which his team won 3–2. The next season, on 23 March 2007, he scored his first Copa Libertadores goals against Caracas at Cúcuta where he netted a hat-trick to a 4–0 away win. On 12 May, Sánchez scored his first and only one league goal during a 3–1 home win over Santiago Wanderers, key in the race for title with Universidad Católica which Colo-Colo finally reached after beat Palestino 1–0 at Monumental the last matchday. Noteworthy, it meant the club's 26th league title. After Sánchez's impressive FIFA U-20 World Cup (where Chile achieved the third place with José Sulantay as coach), his loan with Colo-Colo expired and on 15 August 2007, he joined Argentina's River Plate on loan from Udinese. Udinese After a successful season in Argentina, Sánchez left South America in July 2008 to join Udinese, where he would meet up with Chilean compatriot Mauricio Isla. Sánchez made his non-competitive debut in a 3–0 win over Bassano and was named the man of match. On 14 September, he played his first Serie A match in a 1–0 loss with Juventus and four days later, he made his European debut against Borussia Dortmund. On